Non-destructive testing device for the detection of flaws in solid rocket motors

ABSTRACT

The outer surface of an inflatable bladder is coated with a sensitizing material to make it sensitive to pressure and/or temperature. The bladder is then introduced through the nozzle of a rocket motor and inflated in the cavity. Depending upon the coating, the surface of the bladder becomes marked in a pattern corresponding to the imperfections in the surface of the rocket motor cavity. The bladder is deflated and removed from the rocket motor and inserted in a transparent cavity model and reinflated. The surface of the bladder on which the imperfection pattern marks appear is visually observed through the wall of the transparent model.

United States Patent Geisler N ON-DESTRUCTIVE TESTING DEVICE FOR THEDETECTION OF FLAWS IN SOLID ROCKET MOTORS Inventor: Robert L. Geisler,PO. Box 6037, Ed-

wards, Calif. 93523 Filed: Aug. 28, 1970 Appl. No 67,825

References Cited Primary Examiner-Richard C. Queisser AssistantExaminer-Herbert Goldstein Attorney-Harry A. Herbert, Jr. and ArsenTashjian [5 7] ABSTRACT The outer surface of an inflatable bladder iscoated with a sensitizing material to make it sensitive to pressureand/or temperature. The bladder is then introduced through the nozzle ofa rocket motor and inflated in the cavity. Depending upon the coating,the surface of the bladder becomes marked in a pattern corresponding tothe imperfections in the surface of the rocket motor cavity. The bladderis deflated and removed from the rocket motor and inserted in atransparent cavity model and reinflated. The surface of the bladder onwhich the imperfection pattern marks appear is visually observed throughthe wall of the transparent model.

4 Claims, 7 Drawing Figures P'ATENTEDMAY 16 m2 SHEET 2 OF 2 INVENTOR.F426 4. 651845 BACKGROUND OF THE INVENTION This invention relates to adevice for inspecting the physical condition of the inner bore of asolid fuel rocket motor or any other cavity with a small access port.More particularly, the inven'tion is concerned with providing anon-destructive testing device which is simple and easy to use in thefield and requires no specialized training by the operating personnel.

While x-ray and other non-destructive testing devices are useful at themanufacturing facility, they are often too costly, bulky, orsophisticated for field use in the inspection of solid fuel rocket motorcavities. Many motors are stored in silos or other cramped locationswhere these presently known devices cannot be effectively utilized.

Another drawback of x-ray, ultrasonics and other presently knownnon-destructive testing procedures is that they are generally employedby passing energy from a source external to the motor, through thepropellant grain, to a detection system located inside or on the otherside of the motor. The propellant grain and case often attenuate orscatter this energy reducing the resolution of flaws which may bepresent on the inner bore. Also, there is always a certain danger whenelectrical and magnetic devices are located in close proximity to thehighly inflammable rocket propellant grain.

Other disadvantages which arise when presently known devices areemployed in the field for rocket motor inspection include the high costof the equipment and the specialized skills required to set-up, operate,and interpret the results obtained. At best, the resolution of anydiscovered defects is limited and the results are generally unreliable.The large size and complexity of the heretofore employed devices as wellas the tendency or possibility of inflicting damage to the rocket motorare objectionable features which create problems when field inspectionis required.

SUMMARY OF THE INVENTION This invention provides an extensible bladderor balloon for determining the physical condition of the inner bore of arocket motor or the like and, more particularly, the invention isconcerned with providing a balloon whose surface is treated with apressure or heat sensitive coating and which, when inflated against theinterior surface, receives an imprint or record of any flaws contactingthe balloon.

Accordingly, it is an object of the invention to provide a devicesuitable for the inspection of a solid rocket motor in order to detectflaws in the inner bore. The device is also suitable for the inspectionof other similarly shaped objects having limited access to an innerarea.

Another object of the invention is to provide a device for determiningthe readiness and reliability of solid fuel rocket motors which aredeployed in the field. Flaws in the inner bore of a rocket motor maygenerally impair the proper operation of the motor.

Still another object of the invention is to provide an inspection systemwhich utilizes low cost elements to determine the physical condition ofthe inner bore of a solid rocket motor. The reduction of costs permitslarge numbers of units to be manufactured and distributed foron-the-spot inspection of the rocket motors after being deployed in thefield.

A further object of the invention is to provide an inspection device fordetecting flaws in the cavity of rocket motors which is simple in designand use. The simplicity permits operation of the device by relativelyunskilled personnel with a minimum of previous training or experience.

A still further object of the invention is the provision of aninspection device for determining the inner bore condition of a solidfuel rocket motor especially as to the presence of voids or cracks. Thedevice is also useful to determine the depth of such voids or cracks aswell as their presence.

These and other objects, features and advantages will become moreapparent after considering the following description taken inconjunction with the annexed drawings wherein like numbers are usedthroughout to identify like elements.

DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a view in schematic of the cross-section of a typical solidfuel rocket motor showing the nozzle through which the device isinserted;

FIG. 2A is a cross-section of one type of rocket propellant grain;

FIG. 2B is a cross-section of another type of rocket propellant grain;

FIG. 3A is a schematic view in longitudinal cross-section of the deviceaccording to the invention ready to be inserted into the rocket motorcavity through the nozzle section;

FIG. 3B shows the balloon in the inflated condition in the rocket motorcavity;

FIG. 3C shows the balloon after being marked and deflated ready forremoval from the rocket motor cavity; and

FIG. 3D shows the marked balloon reinflated in the transparent cavitymodel so that the surface markings can be observed.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings,there is schematically shown in longitudinal cross-section, a typicalsolid rocket motor designated generally by the numeral 13. The lower endof the motor 13 is provided with a nozzle 15 which communicates with theinner cavity 17. The propellant grain l9 surrounds the cavity 17 and isenclosed in the motor case 21. In FIGS. 2A and 28 there are showntypical cross-sections of two propellant grains. A circular cavity 17 isshown in FIG. 2A while a more complex star cavity 17 is shown in FIG.2B. The present invention is primarily adapted for determining thephysical condition and presence of flaws on the inner surface of thehollow propellant grain 19.

The system for accomplishing the above-described testing procedure isshown in FIGS. 3A through 3D. A canister 23 is inserted into the nozzle15 of the rocket motor 13. In communication with the canister 23 is agas supply 25 under pressure. A valve'27 is provided in the gas line 29to control the flow of gas to the canister 23. Auxiliary means 31 areprovided for introducing heat or secondary developing gas to the maingas supply 25 as it flows through the line 29. An inflatable bladder orballoon 33 shown in the inflated condition in FIG. 3B is caused to beexpelled from the canister 23 by the pressurized gas from the gas supply25. The balloon 33 is made to fit snugly within the cavity 17 of therocket motor 13 and an image which indicates the physical condition ofthe inner bore is obtained on its outer surface.

The balloon 33 is then deflated, as shown in FIG. 3C, and removed fromthe rocket motor cavity 17. In order to determine the physical conditionof cavity surface, the balloon 33 is inserted into a clear plastic orglass model 35 of the motor cavity and reinflated. Any defect in therocket cavity will show up on the balloon surface as an image 37 of thedefect and can be visually observed through the wall of the transparentcavity model 35.

MODE OF OPERATION The hereinbefore described device for the detection offlaws in the inner cavity of a solid fuel rocket motor provides a simpleand efficient solution to the problem of testing the operating conditionof solid rocket motors deployed in the field.

In operation, the inflatable bladder or balloon 33 is constructed suchthat, upon inflation to a suitable pressure, it is placed in intimatecontact with the interior surface of the cavity 17 to be inspected. Thedrawing, FIGS. 3A through 3D, shows the use of the present invention forthe inspection of the cavity of a typical rocket motor 13. The inventionis also useful for the inspection of other cavities. For example, itcould be used to inspect the inner surface of pipes and vessels used inthe chemical process industry or interiors of nuclear reactor parts. Itcan also be used to inspect the interior of fuel tanks and storagevessels.

In practice, the balloon 33 is coated with a sensitizing material ofwhich many types are available. One such type of coating is pressuresensitive and includes encapsulated dye or ink wherein a color isproduced where the micro capsules are broken by applied force. In thiscase, the coating will be developed" where it contacts the surface andnot developed where it spans a flaw because of the lack of contact forcein these regions. An outline of the flaw is thereby produced between thedeveloped and undeveloped regions. Undesired development" of the coatingduring insertion and extraction is avoided by designing the coating suchthat it can be activated or deactivated during the desired phases of theinspection process. Heat or chemical gases from the auxiliary means 31can be introduced to accomplish this by increasing the pressuresensitivity only during the time when the inserted balloon 33 is incontact with the surface to be inspected.

Temperature sensitive coatings can also be used to produce flaw images37 shown in FIG. 3D. Liquid crystals and thermochromic materials of thistype are well known in the art. The coated balloon 33 is positioned byinsertion into the rocket motor cavity and warm gas is introduced. Heattransfer is greatest at the points of contact with the surface andlowest where the balloon 33 spans the flaw. As the gas temperature isincreased, it will develop the flaw image since it will reach thedevelopment temperature due to its lower heat transfer rate. The balloon33 is then cooled, deflated, and removed. Crack volume or depth can beestimated by taking into account exposure time and total heat flux. Thetotal volume of gas in the flaw can be estimated and hence, its depth.

Another newly developed system for detecting flaws in cavities utilizessound sensitive films. The balloon 33 is coated with a frequencysensitive material which is used to locate flaws and determine theirlength, width and volume. The balloon 33 serves as a membrane over theflaw. When sound waves are generated in the balloon 33, the frequencydependent coating is developed when the resonant frequency of the flawvolume is reached. Thus, through several tests the flaw volume can bebracketed and its depth estimated.

The balloon 33 sensitized in one of the above-described procedures isintroduced through the access port of the rocket nozzle and inflated inthe cavity 17. it is developed and deflated and removed. It is thenreinflated in a transparent model 35 of the cavity for inspection. Thelocation and dimensions of the flaws 37 are then observed and recorded.Future disposition of the inspected object is then determined based uponthese findings. I

Although the invention has been illustrated in the accompanying drawingsand described in the foregoing specification in terms of a preferredembodiment thereof, the invention is not limited to this embodiment orto the particular configuration mentioned. It will be apparent to thoseskilled in the art that my invention could have extensive use in otherinspection and detection operations where it is necessary to providesimple, fast, and reliable equipment for field inspection of theinnersurfaces of limited access cavities.

Having thus set forth and disclosed the nature of my invention, what Iclaim and desire to secure by Letters Patent of the United States is:

l. A testing device for the detection of flaws on the wall of the innercavity of a solid rocket motor comprising, an extensible bladder, asensitive coating disposed on the outer surface of said bladder forproducing a visible image when said bladder is in contact with a surfacecontaining a flaw, a canister for containing said bladder while in acompletely deflated condition, said canister being for positioning inthe nozzle port of the solid rocket motor, pressurized gas means incommunication with the interior: of said bladder in said canister, saidgas means operable to expel said bladder from said canister into thecavity of the solid rocket motor and inflate said bladder until it fitssnugly within the cavity to produce marks on said sensitive coatingwhich correspond to flaws in the cavity wall, and a transparent plasticmodel of the rocket motor cavity for inserting the extensible blatterafter removal from the rocket motor whereby the blatter may bereinflated to expand against the inner walls of said model therebyrevealing, by visual observation, any flaws which are present on theinner surface of the rocket motor cavity and which are imaged on saidsensitive outer surface coating of said extensible bladder.

2. The testing device defined in claim 1 wherein an auxiliary means islocated in a line between said pressurized gas means and said bladderfor introducing heat and secondary developing gas as the gas flowsthrough the line.

3. The testing device defined in claim 2 wherein the sensitive coatingdisposed on the outer surface of said bladder is temperature sensitiveand includes liquid crystals of thermochromic materials wherein an imageof the flaw in the rocket motor cavity is produced when a warm gas isintroduced into said bladder after being inflated to fit snugly withinthe cavity of the solid rocket motor.

4. The testing device defined in claim 1 wherein the sensitive coatingdisposed on the outer surface of said bladder is pressure sensitive andincludes encapsulated dye wherein a color is produced when microcapsules are broken by applied force produced when said bladder isinflated to fit snugly. within the cavity of the solid rocket motor.

1. A testing device for the detection of flaws on the wall of the innercavity of a solid rocket motor comprising, an extensible bladder, asensitive coating disposed on the outer surface of said bladder forproducing a visible image when said bladder is in contact with a surfacecontaining a flaw, a canister for containing said bladder while in acompletely deflated condition, said canister being for positioning inthe nozzle port of the solid rocket motor, pressurized gas means incommunication with the interior of said bladder in said canister, saidgas means operable to expel said bladder from said canister into thecavity of the solid rocket motor and inflate said bladder until it fitssnugly within the cavity to produce marks on said sensitive coatingwhich correspond to flaws in the cavity wall, and a transparent plasticmodel of the rocket motor cavity for inserting the extensible blatterafter removal from the rocket motor whereby the blatter may bereinflated to expand against the inner walls of said model therebyrevealing, by visual observation, any flaws which are present on theinner surface of the rocket motor cavity and which are imaged on saidsensitive outer surface coating of said extensible bladder.
 2. Thetesting device defined in claim 1 wherein an auxiliary means is locatedin a line between said pressurized gas means and said bladder forintroducing heat and secondary developing gas as the gas flows throughthe line.
 3. The testing device defined in claim 2 wherein the sensitivecoating disposed on the outer surface of said bladder is temperaturesensitive and includes liquid crystals of thermochromic materialswherein an image of the flaw in the rocket motor cavity is produced whena warm gas is introduced into said bladder after being inflated to fitsnugly within the cavity of the solid rocket motor.
 4. The testingdevice defined in claim 1 wherein the sensitive coating disposed on theouter surface of said bladder is pressure sensitive and includesencapsulated dye wherein a color is produced when micro capsules arebroken by applied force produced when said bladder is inflated to fitsnugly within the cavity of the solid rocket motor.